This invention relates to the synthesis of N-substituted aminomethylphosphonic acids, and more particularly to an improved process in which an amide, urea or carbamate compound is reacted with phosphorous acid and formaldehyde in an acidic medium to produce an N-substituted aminomethylphosphonic acid.
N-substituted aminomethylphosphonic acids are useful intermediates in the preparation of various products, including sequestering agents and herbicides. Thus, for example, an N-alkyl-N-phosphonomethylamino acid, such as N-isopropyl-N-phosphonomethylglycine, can be dealkylated under alkaline conditions to the corresponding N-phosphonomethylamino acid using the method of the copending and coassigned application of Miller and Balthazor, Ser. No. 687,404 filed Dec. 28, 1984.
N-phosphonomethylglycine, known also by its common name glyphosate, is a highly effective and commercially important phytotoxicant useful in controlling a large variety of weeds. It is applied to the foliage of a very broad spectrum of annual and perennial grasses and broadleaf plants. Industrial uses include control of weeds along roadsides, waterways, transmission lines and in storage areas and other non-agricultural areas. Usually glyphosate is formulated into herbicidal compositions in the form of its various salts in solution, preferably water.
Because of its commercial importance, many processes for making glyphosate have been published. Processes are also known for the preparation of other phosphonomethylated amine compounds. In the former category, for example, is Gaertner U.S. Pat. No. 3,927,080 which describes the preparation of N-t-butyl-N-phosphonomethylglycine by reacting t-butylamine with a bromoacetate ester to produce an ester of N-t-butylglycine, and thereafter reacting the N-t-butylglycine ester with formaldehyde and a dialkyl phosphite to produce esters of N-t-butyl-N-phosphonomethylglycine. The latter product is hydrolyzed under acidic conditions to produce glyphosate.
European patent No. 00 55 695 discloses a process for splitting a 1-arylmethyl group from an N-1-arylalkyl-N-phosphonomethylglycine by hydrogenolytic cleavage. The glyphosate precursor is prepared by reaction of an N-1-arylalkylglycine with phosphorous acid and formaldehyde in an aqueous hydrochloric acid medium.
Pfliegel et al U.S. Pat. No. 4,065,491 describes the preparation of glyphosate directly by condensation of glycine, formaldehyde, and a dialkyl phosphite in an aqueous alkaline medium comprising sodium hydroxide.
Ehrat U.S. Pat. No. 4,237,065 describes a synthesis substantially similar to that disclosed in Pfliegel et al. However, Ehrat carries out the reaction using a tertiary amine base in an alcohol medium rather than the sodium hydroxide solution utilized by Pfliegel et al.
Irani and Moedritzer U.S. Pat. No. 3,288,846 also describes the reaction of other nitrogen compounds such as ammonia, or a primary or secondary amine, with an aldehyde or ketone and phosphorous acid to form an aminoalkylenephosphonic acid. However, unlike the processes disclosed by Pfliegel et al and Ehrat, the Irani process is carried out in an aqueous medium having a pH below about 4.
Shin et al U.S. Pat. No. 3,567,768 describes the preparation of an aminoalkylenephosphonic acid compound by reaction of a reactive nitrogenous material (i.e., a nitrogen containing or nitrogenous compound such as ammonia, a primary amine, or secondary amine), an aldehyde or ketone, and an excess of phosphorous acid. Where the nitrogenous reactant is ammonia or an ammonium salt, the product is the same as that prepared in accordance with the Krueger patent, discussed below. The exemplary disclosure of Shin describes a preparation in which phosphorous acid is premixed with ammonium chloride and water, and the resultant mixture is heated to reflux while formaldehyde is added thereto.
Japanese Pat. No. Sho 47[1972]-112 describes a method for the treatment of cellulose fibers with a solution which is prepared by the reaction of a nitrogen compound, phosphorous acid, and formalin. The nitrogen compound is one which contains two or more amino groups, such as for example, urea, thiourea, guanidine, or an alkyldiamide. However, the reference is concerned with enhancing the characteristics of the treated fiber and contains no disclosure of the structure of any product that may be formed by reaction of the aforesaid materials. Nor does the reference report any analytical work which might provide an indication of the structure of such product.
Krueger et al. U.S. Pat. No. 4,009,204 describes the preparation of nitrilo tris(methylenephosphonic acid) by reaction of an aliphatic amide with formaldehyde and a phosphorus trihalide. In the Krueger process, the amide substrate is preferably premixed with the aldehyde and the phosphorus trihalide added dropwise thereto. Alternatively, the aldehyde and phosphorus trihalide are premixed, and the acid amide slowly added to the latter premixture.
Various processes are known in the art for the preparation of amides, carbamates, and ureas. French Pat. No. 2,523,576 describes a method for preparing N-acyliminodiacetic acid by reaction of an unsubstituted amide with formaldehyde and carbon monoxide in the presence of a carbonylation catalyst. Provision of a method for conversion of the N-acyliminodiacetic acid to N-phosphonomethyliminodiacetic acid would establish an advantageous route to glyphosate, since Hershman U.S. Pat. No. 3,969,398 describes a process for preparation of glyphosate by oxidation of N-phosphonomethyliminodiacetic acid in the presence of activated carbon, and Franz U.S. Pat. No. 3,950,402 describes a similar process using a noble metal on carbon as a catalyst. The disclosure of Miller and Balthazor, Ser. No. 687,404 filed Dec. 28, 1984 describes the phosphonomethylation of N-isopropylglycine to N-isopropylglyphosate and conversion of the latter intermediate to glyphosate by dealkylation in an alkaline medium.
Other processes are available for the preparation of a wide variety of substituted and unsubstituted amides, carbamates, and ureas corresponding to the formula: ##STR1## where typically R is hydrogen, alkyl, cycloalkyl, aryl, carboxyalkyl, alkoxy, aryloxy, or amino, R.sup.1 and R.sup.2 are independently selected from among hydrogen, alkyl, cycloalkyl, aryl, arylalkyl, and carboxyalkyl, and X is oxygen or sulfur.
The copending and coassigned application of Reitz, (Ser. No. 687,327 filed Dec. 28, 1984) describes a novel and advantageous method for the preparation of various amides.